Re: [Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m
I’ve seen no mention of modeling and/or measurements performed on any of these antennas to see if they are within the match range of the KPA1500. Jim ab3cv On Sep 4, 2020, at 2:29 AM, Victor Rosenthal 4X6GP wrote: I had an interesting experience trying to use a balun in a very demanding situation. I'll describe it, and at the end I have a question. Antenna was a dipole with total length of 10m fed with approximately 480 ohm open-wire line. Line length was 10m. I was trying to use this antenna on 40m with a power of 1200w. The first attempt was to use a 5kw DX Engineering 1:4 balun in the shack between the open line and coax, feeding the coax with an unbalanced T-network tuner. There was a lot of RFI with computers, etc. in the shack. The antenna seemed to pick up a lot of local noise. During a period of contest operating, the balun overheated, causing soaring SWR and ultimately internal arcing. Next I added two capacitors in series with the line to tune out the reactance (the 1/4 wavelength line inverted the capacitive reactance at the feedpoint of the antenna making it inductive at the shack end). This eliminated the overheating (it ran a little warm), but the RFI problem remained. Then I rewired the balun to a 1:1 configuration. This seemed to help a little with the RFI. It made tuning easier. But the antenna was still noisy. At this point I had some really good luck and was able to purchase an old Johnson KW Matchbox, which is a link-coupled balanced tuner. I replaced the T-network tuner, the balun, and the series capacitors with this unit. The antenna is now MUCH quieter and RFI problems have been eliminated. The lesson I learned is that baluns don't work very well with high SWR, especially when the impedance is very reactive. And now for my question: did I permanently damage my balun when it overheated? If so, what is the mechanism of damage? I took it apart and didn't see any obvious signs. 73, Victor, 4X6GP Rehovot, Israel Formerly K2VCO CWops no. 5 http://www.qsl.net/k2vco/ . > On 03/09/2020 19:05, Jim Brown wrote: > A choke inserted into a poorly > matched or un-matched line is much more likely to overheat and fail. > Dissipation (heating) is addressed in the 2018 Cookbook. > 73, Jim K9YC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to j...@jtmiller.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m
I had an interesting experience trying to use a balun in a very demanding situation. I'll describe it, and at the end I have a question. Antenna was a dipole with total length of 10m fed with approximately 480 ohm open-wire line. Line length was 10m. I was trying to use this antenna on 40m with a power of 1200w. The first attempt was to use a 5kw DX Engineering 1:4 balun in the shack between the open line and coax, feeding the coax with an unbalanced T-network tuner. There was a lot of RFI with computers, etc. in the shack. The antenna seemed to pick up a lot of local noise. During a period of contest operating, the balun overheated, causing soaring SWR and ultimately internal arcing. Next I added two capacitors in series with the line to tune out the reactance (the 1/4 wavelength line inverted the capacitive reactance at the feedpoint of the antenna making it inductive at the shack end). This eliminated the overheating (it ran a little warm), but the RFI problem remained. Then I rewired the balun to a 1:1 configuration. This seemed to help a little with the RFI. It made tuning easier. But the antenna was still noisy. At this point I had some really good luck and was able to purchase an old Johnson KW Matchbox, which is a link-coupled balanced tuner. I replaced the T-network tuner, the balun, and the series capacitors with this unit. The antenna is now MUCH quieter and RFI problems have been eliminated. The lesson I learned is that baluns don't work very well with high SWR, especially when the impedance is very reactive. And now for my question: did I permanently damage my balun when it overheated? If so, what is the mechanism of damage? I took it apart and didn't see any obvious signs. 73, Victor, 4X6GP Rehovot, Israel Formerly K2VCO CWops no. 5 http://www.qsl.net/k2vco/ . On 03/09/2020 19:05, Jim Brown wrote: A choke inserted into a poorly matched or un-matched line is much more likely to overheat and fail. Dissipation (heating) is addressed in the 2018 Cookbook. 73, Jim K9YC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m
I do the same Rick. However, when new firmware comes out, I update my manuals appropriately. Elecraft allows that, unlike Icom, Kenwood, or Yaesu. I wonder why? Refreshing my own "firmware" is much more challenging, especially for things not refreshed by use. Many questions on this reflector are already answered in the Elecraft manuals. Watching my P3, I find many, many SSB signals over-driven with, I'll bet, ALC way out of range, even on an occasional Elecraft rig. When I send them a screenshot, or mention it on-the-air, frequently, the operator can't find the ALC reading. RTFM! I'm hoping the lightning stays away (for a change) during this weekend's QSO parties. 73, Bill, K8TE -- Sent from: http://elecraft.365791.n2.nabble.com/ __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m
Being able to use a without reading the manual is actually one of my personal tests of the user interface. Jump in, see how it plays and what is presented to make changes if needed. The K3 easily passes that test (former Kenwood user; Elecraft is similar in format), HOWEVER that is on the surface only. One must read through the manual (a few times preferably) to get into the menu settings (only one layer deep) and the reasons for them, when to apply them. An annual or topical review can be done in personal down time, to keep the meat memory cells active. And even then, something new may 'appear' in the text and learning happens. Then for reading dessert, read the firmware update statements as a few things are added and others change slightly over time since the manual was created. I also have a 7300 (for the RV) and it's not as UI friendly to me but is a convoluted series of menus to alter what should be a simple change; so it's what one is used to seeing, in part. Some of that is cross-cultural phrasing, some of it, is a lesser UI (in my opinion). 73, Rick NK7I K3, P3, KAT500, KPA500, KPA1500, investments in quality. On 9/3/2020 11:56 AM, K8TE wrote: RTFM is a wonderful acronym to follow. I'm always surprised to read "I think..." "I recall..." and similar posts to answer a poster's question. Most of us are U.S.A. males, no offense to those who aren't. As such, our DNA has been irradiated by past (not Cycle 24) solar cycles and we no long see the need to read manuals. A friend of mine bought an IC-7300 because he could operate it without reading the manual. He has since read some of the manual and uses features that make his signal (usually weak with a 12 ft. high antenna) more copyable. I am working on his further conversion. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m
That is not true, except at full power. The manual clearly states power levels at 10:1, 5:1, and 4:1 VSWR's for different frequency ranges. RTFM is a wonderful acronym to follow. I'm always surprised to read "I think..." "I recall..." and similar posts to answer a poster's question. Most of us are U.S.A. males, no offense to those who aren't. As such, our DNA has been irradiated by past (not Cycle 24) solar cycles and we no long see the need to read manuals. A friend of mine bought an IC-7300 because he could operate it without reading the manual. He has since read some of the manual and uses features that make his signal (usually weak with a 12 ft. high antenna) more copyable. I am working on his further conversion. May the mask be with you! (COVID-19) 73, Bill, K8TE -- Sent from: http://elecraft.365791.n2.nabble.com/ __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m
Hi Jim Thanks for the new link. I must say we made several big chokes using the "old" method and our analyser wasn't good enough to measure the common mode impedance, so our conclusion was they were all above the analyser limit of several thousand ohms. I'm about to make a single core choke, so I'll take a look at the new info. 73 David G3UNA > On 03 September 2020 at 17:05 Jim Brown wrote: > > > On 9/3/2020 4:21 AM, CUTTER DAVID via Elecraft wrote: > > I use K9YC-style chokes, eg several turns on 240-31 core, or, if it's > > really bad, several turns on several cores using 7" diameter turns (from > > memory, check his cookbook). I'm told this is cheaper and better than > > anything you can buy. Of course I know nothing about your layout but it > > has always helped me to ground the coax before it comes into the house. > > Hi David, > > Note that, based on extensive research in 2017 and 2018, I no longer > recommend the older style of choke that you're using, and I revised the > RFI tutorial to reflect that. I published both that revision and the new > Cookbook late in 2018. > > k9yc.com/publish.htm > > The problem with the older style chokes (multiple turns of coax on > multiple #31 cores) is that 1) any "scrambling" of the winding reduces > choking impedance, and 2) variations in winding style (diameter, > spacing) make the chokes non-repeatable. > > The new choke designs ARE repeatable, AND take into account the wide > manufacturing tolerances of all ferrite parts, which can significantly > affect the choking impedance and where the chokes are tuned. The work I > did in 2017 and 2018 included characterizing nearly 200 #31 cores > obtained from multiple vendors over about ten years, selecting cores at > the limits of those tolerances, winding and measuring hundreds of chokes > on those cores, tabulating the results, and making recommendations for > each band and each transmission line type based on worst case results > for each design. Chokes wound following the new 2018 Cookbook should > provide at least the specified response on any #31 core you buy. Note > that #31 mix is made ONLY by Fair-Rite. > > Another point about measuring common mode current. As you have observed, > it varies along the line, simply because in the common mode circuit, the > feedline is part of the antenna, and both voltage and current vary along > the line conforming to wavelength relationships at the operating > frequency. A good choke forces a current minimum at the point where it > is inserted. How common mode current varies along the line depends on > the quality of the choke, the electrical length of the outer conductor > of the coax (VF~0.98), and how the shield is terminated on the other end > (grounded or floating using a link coupled tuner). > > A choke is most useful at the antenna feedpoint (up in the air, or at > the feed end of a vertical or other long wire), which tends to minimize > common mode current all along the line, because it "disconnects" the > feedline from the antenna. A choke at any other point is FAR less > effective -- all it does force a current minimum at the point it is > inserted, leaving the feedline connected to the antenna, allowing common > mode current between the choke and the antenna, and coupling any noise > current to the antenna. > > For this reason, the first choke in any system should ALWAYS be at the > antenna IF the antenna is matched to the feedline. The power handling of > my chokes are ONLY applicable if the feedline is matched at the point > where they are inserted. A choke inserted into a poorly matched or > un-matched line is much more likely to overheat and fail. Dissipation > (heating) is addressed in the 2018 Cookbook. > > 73, Jim K9YC > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to d.cut...@ntlworld.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m
On 9/3/2020 4:21 AM, CUTTER DAVID via Elecraft wrote: I use K9YC-style chokes, eg several turns on 240-31 core, or, if it's really bad, several turns on several cores using 7" diameter turns (from memory, check his cookbook). I'm told this is cheaper and better than anything you can buy. Of course I know nothing about your layout but it has always helped me to ground the coax before it comes into the house. Hi David, Note that, based on extensive research in 2017 and 2018, I no longer recommend the older style of choke that you're using, and I revised the RFI tutorial to reflect that. I published both that revision and the new Cookbook late in 2018. k9yc.com/publish.htm The problem with the older style chokes (multiple turns of coax on multiple #31 cores) is that 1) any "scrambling" of the winding reduces choking impedance, and 2) variations in winding style (diameter, spacing) make the chokes non-repeatable. The new choke designs ARE repeatable, AND take into account the wide manufacturing tolerances of all ferrite parts, which can significantly affect the choking impedance and where the chokes are tuned. The work I did in 2017 and 2018 included characterizing nearly 200 #31 cores obtained from multiple vendors over about ten years, selecting cores at the limits of those tolerances, winding and measuring hundreds of chokes on those cores, tabulating the results, and making recommendations for each band and each transmission line type based on worst case results for each design. Chokes wound following the new 2018 Cookbook should provide at least the specified response on any #31 core you buy. Note that #31 mix is made ONLY by Fair-Rite. Another point about measuring common mode current. As you have observed, it varies along the line, simply because in the common mode circuit, the feedline is part of the antenna, and both voltage and current vary along the line conforming to wavelength relationships at the operating frequency. A good choke forces a current minimum at the point where it is inserted. How common mode current varies along the line depends on the quality of the choke, the electrical length of the outer conductor of the coax (VF~0.98), and how the shield is terminated on the other end (grounded or floating using a link coupled tuner). A choke is most useful at the antenna feedpoint (up in the air, or at the feed end of a vertical or other long wire), which tends to minimize common mode current all along the line, because it "disconnects" the feedline from the antenna. A choke at any other point is FAR less effective -- all it does force a current minimum at the point it is inserted, leaving the feedline connected to the antenna, allowing common mode current between the choke and the antenna, and coupling any noise current to the antenna. For this reason, the first choke in any system should ALWAYS be at the antenna IF the antenna is matched to the feedline. The power handling of my chokes are ONLY applicable if the feedline is matched at the point where they are inserted. A choke inserted into a poorly matched or un-matched line is much more likely to overheat and fail. Dissipation (heating) is addressed in the 2018 Cookbook. 73, Jim K9YC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m
, but > > as I tried to remove the braid, it was obvious that there had been > > considerable heating as the center section of the braid has melted into the > > center conductor insulation, and somewhere in there, it has made it right > > through to the center conductor. > > > > Unfortunately I haven't yet found the exact point of the short, because I > > left the partly dismantled piece of inner co-ax on a table and one of my > > cats seems to have run off with it! :-D > > When I eventually find it, I'll continue investigating. > > > > In the meantime, one theory is that the common mode choke presented a high > > impedance to RF coming back down the co-ax and this in turn produced a very > > high voltage causing an arc between inner and outer and as the > > characteristics changed, in turn a high current node was created, which > > caused the heating effect. Another theory is that it is just a crappy piece > > of cable and it just failed. > > > > Unfortunately this is not the sort of fault that can be detected in its > > development stage by a low power antenna analyser, it needs a fair amount > > of power. > > > > This long tale may just give you some clues to your possible issue on 160m > > although on a different power scale.. > > > > 73, > > > > Alan. G4GNX > > > > > > -- Original Message -- > > From: "Ken Ramirez de Arellano" > > To: elecraft@mailman.qth.net > > Sent: 02/09/2020 22:41:30 > > Subject: [Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m > > > >> Every bit of antenna hardware ( coax, balun, insulators, etc. have been > >> changed out or proven good. Connections are all solid. My KPA1500 will > >> transmit above 800 watts for about 15-30 seconds and then the SWR jumps up > >> and it faults out for high VSWR. I can run 1500 watts on all the other > >> “Legacy” bands (10,15,20,40,80) with no problems. I’ve forced an STU > >> relearn and still the same issue. The antenna B amp is a Clipperton L and > >> that transmits at a KW out and I see no change in VSWR in the external > >> wattmeter using all of the same cabling. It’s starting to look like > >> something heating up in the KPA1500. Is anyone aware of a known issue for > >> this with the KPA1500 or a known fix? I would rather do a field repair > >> instead of sending to Elecraft from KP4. TIA Ken, KP3MM > >> -- > >> Ken Ramirez > >> KP3MM > >> > > > > __ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:Elecraft@mailman.qth.net > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > Message delivered to w5...@comcast.net > > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to d.cut...@ntlworld.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
[Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m
KPA1500 tuner is rated for maximum antenna SWR of just 3 to 1. 73, Roy K6XK __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m
Update I took the Balun designs 4:1 out of line and put a Dx Engineering maxi core 5kw 4:1 in its place. It tunes a little better on 160 but the KPA1500 finally faults out and says cannot find match and shows 9:1 better than 99:1 So I put the KPA1500 straight to a 2.5kw bird dummy load and it tunes instantly 1:1 in 160M So this fault is with the antenna for sure The only other Balun I have to try is a DX Engineering 6:1 which I will try in the morning. Failing that I will order a 1:1 feom DX Engineering But at least I know it’s the antenna that is causing this problem I’m going to also borrow a antenna analyzer tomorrow and see what gives. Thanks for all the suggestions! We will whip this yet Ronnie w5sum Sent from my iPhone > On Sep 2, 2020, at 6:05 PM, Alan - G4GNX wrote: > > Ken, sorry this is rather long, but here goes... > > I had a similar problem in the UK, with a OSCFD antenna, purchased from a UK > company. I didn't question the theory and just assembled it according to > instructions. > > As you would expect the antenna is made from two differing lengths of > ruggedised, plastic coated copper wire, which is fed by a 4:1 Guanella balun, > rated at 400W. The balun is potted in a weatherproof box and is fed via the > customary PL259/SO239 connector with Mil Spec RG58 coaxial cable. About 6' > down from the feed point is a common mode choke (sometimes called a sleeve > balun) which consists of 8 ferrite inline cores, around the co-ax and held in > place with heat shrink sleeving and cable ties. > > The rig was just the K3S/100W with internal tuner and all was well for many > months, mostly using 40 metres SSB. A while later, I added the KPA500/KAT500 > combo which I ran for a couple of very short periods at 400W to test. For a > weekly net, I used only 200W and all seemed OK for a while, until suddenly > the VSWR started to increase over the period of an 'over'. Over a few weeks > this got more frequent and I would have to re-tune part way through an > 'over'. At that time, I wan't sure whether it was an antenna issue, or the > KPA500/KAT500, although I suspected that the KPA500 was getting too hot, so I > posted a question on a forum and was contacted by Jack Brindle of Elecraft, > who kindly looked at the KPA500 fault reports and sent me a comprehensive > explanation of his findings based on the figures and his experience, which > concluded that the antenna was almost certainly the culprit. > > I ordered a new 1KW Guanella balun and some much bigger ferrites, with the > intention of replacing the RG58 with Westflex 103. In the meantime I > soldiered on with the original setup until one day all hell let loose, with > the KPA500 and KAT500 fault lights flashing and even the K3S got 'ticked > off'. At this point I switched to my HF vertical, to keep me on the air. > > When I dismantled the wire antenna, I expected a balun fault, but it was > actually OK. On further checking, after disconnecting the co-ax from the > balun, the open ended co-ax showed a DC short on a test meter! > > I used the Rig Expert 600 to determine exactly where the short was and it > turned out to be exactly where the sleeve ferrites had been, BUT there was no > discoloration of the outer covering, or signs of melting, so I knew it was > unlikely that the ferrite cores had got heated. I cut the section out of the > co-ax and started to take it apart. With the outer covering all removed, > there was still no sign of discoloration of the screen braid, but as I tried > to remove the braid, it was obvious that there had been considerable heating > as the center section of the braid has melted into the center conductor > insulation, and somewhere in there, it has made it right through to the > center conductor. > > Unfortunately I haven't yet found the exact point of the short, because I > left the partly dismantled piece of inner co-ax on a table and one of my cats > seems to have run off with it! :-D > When I eventually find it, I'll continue investigating. > > In the meantime, one theory is that the common mode choke presented a high > impedance to RF coming back down the co-ax and this in turn produced a very > high voltage causing an arc between inner and outer and as the > characteristics changed, in turn a high current node was created, which > caused the heating effect. Another theory is that it is just a crappy piece > of cable and it just failed. > > Unfortunately this is not the sort of fault that can be detected in its > development stage by a low power antenna analyser, it needs a fair amount of > power. > > This long tale may just give you some clues to your possible issue on 160m > although on a different power scale.. > >
Re: [Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m
Ken, sorry this is rather long, but here goes... I had a similar problem in the UK, with a OSCFD antenna, purchased from a UK company. I didn't question the theory and just assembled it according to instructions. As you would expect the antenna is made from two differing lengths of ruggedised, plastic coated copper wire, which is fed by a 4:1 Guanella balun, rated at 400W. The balun is potted in a weatherproof box and is fed via the customary PL259/SO239 connector with Mil Spec RG58 coaxial cable. About 6' down from the feed point is a common mode choke (sometimes called a sleeve balun) which consists of 8 ferrite inline cores, around the co-ax and held in place with heat shrink sleeving and cable ties. The rig was just the K3S/100W with internal tuner and all was well for many months, mostly using 40 metres SSB. A while later, I added the KPA500/KAT500 combo which I ran for a couple of very short periods at 400W to test. For a weekly net, I used only 200W and all seemed OK for a while, until suddenly the VSWR started to increase over the period of an 'over'. Over a few weeks this got more frequent and I would have to re-tune part way through an 'over'. At that time, I wan't sure whether it was an antenna issue, or the KPA500/KAT500, although I suspected that the KPA500 was getting too hot, so I posted a question on a forum and was contacted by Jack Brindle of Elecraft, who kindly looked at the KPA500 fault reports and sent me a comprehensive explanation of his findings based on the figures and his experience, which concluded that the antenna was almost certainly the culprit. I ordered a new 1KW Guanella balun and some much bigger ferrites, with the intention of replacing the RG58 with Westflex 103. In the meantime I soldiered on with the original setup until one day all hell let loose, with the KPA500 and KAT500 fault lights flashing and even the K3S got 'ticked off'. At this point I switched to my HF vertical, to keep me on the air. When I dismantled the wire antenna, I expected a balun fault, but it was actually OK. On further checking, after disconnecting the co-ax from the balun, the open ended co-ax showed a DC short on a test meter! I used the Rig Expert 600 to determine exactly where the short was and it turned out to be exactly where the sleeve ferrites had been, BUT there was no discoloration of the outer covering, or signs of melting, so I knew it was unlikely that the ferrite cores had got heated. I cut the section out of the co-ax and started to take it apart. With the outer covering all removed, there was still no sign of discoloration of the screen braid, but as I tried to remove the braid, it was obvious that there had been considerable heating as the center section of the braid has melted into the center conductor insulation, and somewhere in there, it has made it right through to the center conductor. Unfortunately I haven't yet found the exact point of the short, because I left the partly dismantled piece of inner co-ax on a table and one of my cats seems to have run off with it! :-D When I eventually find it, I'll continue investigating. In the meantime, one theory is that the common mode choke presented a high impedance to RF coming back down the co-ax and this in turn produced a very high voltage causing an arc between inner and outer and as the characteristics changed, in turn a high current node was created, which caused the heating effect. Another theory is that it is just a crappy piece of cable and it just failed. Unfortunately this is not the sort of fault that can be detected in its development stage by a low power antenna analyser, it needs a fair amount of power. This long tale may just give you some clues to your possible issue on 160m although on a different power scale.. 73, Alan. G4GNX -- Original Message -- From: "Ken Ramirez de Arellano" To: elecraft@mailman.qth.net Sent: 02/09/2020 22:41:30 Subject: [Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m Every bit of antenna hardware ( coax, balun, insulators, etc. have been changed out or proven good. Connections are all solid. My KPA1500 will transmit above 800 watts for about 15-30 seconds and then the SWR jumps up and it faults out for high VSWR. I can run 1500 watts on all the other “Legacy” bands (10,15,20,40,80) with no problems. I’ve forced an STU relearn and still the same issue. The antenna B amp is a Clipperton L and that transmits at a KW out and I see no change in VSWR in the external wattmeter using all of the same cabling. It’s starting to look like something heating up in the KPA1500. Is anyone aware of a known issue for this with the KPA1500 or a known fix? I would rather do a field repair instead of sending to Elecraft from KP4. TIA Ken, KP3MM -- Ken Ramirez KP3MM __ Elecraft mailing list Home: http://mailman.qth.net/mailma
Re: [Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m
If your Clipperton amp doesn't have the same problem then it does indeed point to the KPA1500. I don't own a KPA1500, but a quick look at the online manual shows that the tuning unit is an L-Network. Depending upon the load the unit is trying to match, an L-Network can require a very large amount of capacitance, especially on 160m ... which I suspect is achieved in the KPA1500 by switching in high power ceramic units for 160m. I had to replace a couple of high power ceramic doorknob capacitors for 160m in my own tube amp because I had degraded them with a high VSWR per my earlier post about an overheating common mode choke. Of course you might not have the same problem, but it would be one of the things I'd check. 73, Dave AB7E On 9/2/2020 2:41 PM, Ken Ramirez de Arellano wrote: Every bit of antenna hardware ( coax, balun, insulators, etc. have been changed out or proven good. Connections are all solid. My KPA1500 will transmit above 800 watts for about 15-30 seconds and then the SWR jumps up and it faults out for high VSWR. I can run 1500 watts on all the other “Legacy” bands (10,15,20,40,80) with no problems. I’ve forced an STU relearn and still the same issue. The antenna B amp is a Clipperton L and that transmits at a KW out and I see no change in VSWR in the external wattmeter using all of the same cabling. It’s starting to look like something heating up in the KPA1500. Is anyone aware of a known issue for this with the KPA1500 or a known fix? I would rather do a field repair instead of sending to Elecraft from KP4. TIA Ken, KP3MM __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
[Elecraft] KPA-1500 SWR fault above 700-800 watts on 160m
Every bit of antenna hardware ( coax, balun, insulators, etc. have been changed out or proven good. Connections are all solid. My KPA1500 will transmit above 800 watts for about 15-30 seconds and then the SWR jumps up and it faults out for high VSWR. I can run 1500 watts on all the other “Legacy” bands (10,15,20,40,80) with no problems. I’ve forced an STU relearn and still the same issue. The antenna B amp is a Clipperton L and that transmits at a KW out and I see no change in VSWR in the external wattmeter using all of the same cabling. It’s starting to look like something heating up in the KPA1500. Is anyone aware of a known issue for this with the KPA1500 or a known fix? I would rather do a field repair instead of sending to Elecraft from KP4. TIA Ken, KP3MM -- Ken Ramirez KP3MM __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
